Apparatus for fabricating gravure printing cylinders with synthetic resin surface

ABSTRACT

A method and an apparatus for fabricating gravure printing cylinders of synthetic resin in which a photosetting polyamide resin used as a solution of a coating resin is applied over the surface of a cylindrical base spirally as successively overlaid layers and thereafter the applied resin is subjected to drying by a heater and to photosetting by irradiation with ultraviolet rays, electron rays or the like. The resin layer surface thus obtained is mechanically engraved by an electronic engraver for forming gravure cells. The irradiation of ultraviolet ray, electron ray, or the like may be effected during or after application of the polyamide resin over the cylindrical base. The apparatus comprises a resin solution retainer closely adjacent to the cylindrical base. A substantially vertical lever pivoted for movement toward and away from the base supports the solution retainer. The lever may be moved by an element such as a motor-driven eccentric cam.

This is a division of application Ser. No. 170,156 filed July 18, 1980,U.S. Pat. No. 4,339,472.

BACKGROUND OF THE INVENTION

This invention relates to an apparatus for fabricating gravure printingcylinders with a synthetic resin surface, having excellent engravingquality, wear resistance, and solvent resistance.

In recent years, with developments in electronics, automatic and preciseetching of gravure cylinders by means of electronic engravers is cominginto wide practice.

In addition to the conventional gravure cylinders entirely made ofmetal, gravure cylinders with a printing surface made of synthetic resinare entering into this field.

Heretofore, for making gravure cylinders, wide use has been made of theso-called "conventional" method, which comprises the steps of plating acopper layer over a cylindrical base, placing an exposed carbon tissuehaving a latent image over the copper layer, developing the carbontissue, etching the cylinder through the carbon tissue, thereafterstripping the tissue from the layer, and chromium plating thetissue-stripped cylinder. This method involves pollution problems sinceit includes chemical treatment processes, such as plating and etchingprocesses, and further, the method necessitates highly skilled art andlabor for forming gravure cells as the etching is made by the use of thecarbon tissue.

The electronic engraver simplifies the etching process, and theformation of the printing surface with resin eliminates the platingprocesses. On these points, the method of fabricating gravure cylindersin which the resin coated over the printing surface is engraved by anelectronic engraver is being developed as an excellent method for makinggravure printing plates.

However, such resin-coated gravure printing cylinders are inferior inproductivity and have not yet satisfied the requirements for the gravureprinting, such as engraving quality, wear resistance, and solventresistance.

Conventionally, vinylchloride resins, ABS resins, aliphatic polyamideresins, and the like are used for the gravure cylinder coating. Withrespect to polyamide resins, an alcohol-soluble polyamide such ascopolymer nylon, and modified nylon can be dissolved in a solvent andcaused to adhere to a cylindrical base by a method called the bladecoater method but has very low solvent resistance against the gravureink. On the other hand, nylon 6, 66, 610, 11, 12 and the like havesolvent resistance, but it is difficult for these resins to be dissolvedin a solvent to be coated over the gravure cylinder. Under the existingcircumstances, with respect to the polyamide resin, the use of theplastic molding method utilizing its thermoplasticity and powder coatingmethod is being tried. These methods, however, necessitate rather largeapparatus and have further disadvantages in the production of thegravure cylinder such as the necessity of surface smoothing by means ofa super-precision lathe after adhesion of the resin.

Vinylchloride resin can be also caused to adhere to the cylindrical baseby the above mentioned blade coater method but requires degassing andsurface smoothing processes. Further, the finished coating has lowsolvent resistance and accordingly is greatly restricted in the printingconditions such as the use of water-base gravure ink.

In addition, all gravure printing cylinders with printing surfaces madeof the foregoing resins by the aforementioned methods have relativelylow wear resistance. That is, the gravure printing cylinders are easilyscratched by impurities in the ink and on the doctor blade, dust and thelike, almost all cylinders being damaged during printing of web of lessthan 10,000 meters long, and it is difficult to apply these cylinders tolarge lot printing of more than 100,000 meters long. In the attempt toimprove the wear resistance, the doctor blade is being made of syntheticresin but is inferior in edge accuracy, edge machining property, inkscraping property, etc., and lacks utility.

The foregoing synthetic resins also have inferior engraving property.More specifically, the engraving of the pattern of an original by theengraving needle is likely to produce burrs and breaks around the cells.Since such burrs can be the cause of scumming, a knife called a burrcutter is provided in the electronic photoengraving machine for scrapingaway the burrs. However, the operation of the burr cutter can cause thesmooth surface of the non-image area to suffer scratches, and thus aburr cutter itself becomes a cause of scumming.

Accordingly, it is desirable that the resin layer has an engravingproperty which makes a burr cutter unnecessary.

SUMMARY OF THE INVENTION

It is accordingly an object of the invention to provide a novelapparatus for fabricating gravure cylinders which have excellent wearresistance and solvent resistance and are capable of large-lot printing.

It is a further object of the invention to provide a novel apparatus forfabricating gravure cylinders that can be uniformly levelled to preventundulations, scratches or the like from being produced thereby tosimplify or eliminate the subsequent smoothing process and to obtainwith high precision the smoothness of the printing surface required forthe gravure printing.

It is another object of the invention to provide a novel apparatus formaking gravure cylinders that have excellent engraving properties andare almost completely free of burrs, breaks, etc., thereby to affordexcellent tone reproduction, and to make unnecessary a burr cutter forthe electronic engraver, which means assurance of a higher tonereproductivity because the scratches or abrasions which have beenproduced by the conventional burr cutter can be avoided.

These and other objects of the invention are achieved by a apparatus forfabricating gravure printing cylinders having a printing surface ofsynthetic resin, in which a photosetting-polyamide resin solution isapplied spirally over the surface of a cylindrical base and subjected todrying by a heater and to photosetting by irradiating thereof withultraviolet rays, electron rays, or the like, and the set resin layersurface thus obtained is mechanically engraved with an electronicengraver to form gravure cells. This method increases the productivityin the production of the gravure printing cylinder and further providesgravure cylinders of excellent engraving property, and wear and solventresistances.

While the specification concludes with claims which particularly pointout and distinctly define the subject matter which is regarded as theinvention, it is believed the invention will be more clearly understoodfrom the following detailed description and the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawing:

FIG. 1 is a diagrammatic perspective view illustrating the step ofapplying resin solution;

FIG. 2 is a diagrammatic side view showing how the resin solution isapplied spirally;

FIG. 3 is a diagrammatic side view showing the step of setting the resinlayer; and

FIG. 4 is a side view illustrating an apparatus for applying the resinsolution.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates the principle of the fabrication of a gravurecylinder having a synthetic resin printing surface consisting of anendless resin layer according to the present invention.

In the fabrication of the gravure cylinder, a cylindrical base 10 isprepared from a material selected from various materials. The base 10may be an iron core having its surface provided with a hard layer ofcopper plating or the like, a core having an elastic layer coated on itssurface, or a core made almost entirely of synthetic resin. Aphotosetting polyamide resin solution 12 is applied as a coating ontothis base 10, in which step, the base is heated to about 40° to 50° C.for facilitating adhesion of the resin solution.

The photosetting polyamide resin solution 12 is prepared by dissolvingin an alcohol a solid resin component comprising a polyamide to which aphotopolymeric monomer, a photopolymerization initiator, and otheradditives have been added.

The resin solution 12 is applied by a coating device 13 to form a spirallayer 14 as shown in FIG. 2. The resin solution is used preferably inthe state of low viscosity, e.g., 10-400 cps, preferably 40-100 cps at25° C. This low viscosity is required for applying precisely a thin filmby the coating device over the surface of the base 10 thereby avoidingundulations, bubbles, scratches, and other defects.

In the coating device 13 shown, a roller-type resin solution retainer16, which can be either nonrotatable or reversely rotated relative tothe base 10, is used. The solution 12 is supplied between the retainer16 and the base 10 as indicated by arrow B. An air-currentless heatdryer 18, preferably containing a farinfrared ray generating heater, isused for drying. The dryer 18 has an arcuate shape and is disposed onthe side of the base 10 remote from the retainer 16. The base 10 isrotated counterclockwise, and the retainer 16 is gradually moved bysuitable means such as that shown in FIG. 4 in the direction of arrow Ashown in FIG. 1, to enable the spiral application of the photosettingsolution 12 over the surface of the base 10. The solution 12 thusapplied is dried quickly by radiant heat from the dryer 18 as the base10 rotates and substantially fully dried during one turn of the base toform a dried layer of the photosetting polyamide resin. As a result, anendless resin layer 14 with a thickness of about 50 to 500 μ is formedon the base surface.

After the above described applying and drying processes, the base 10 ismoved to another place and rapid setting of the resin layer is carriedout at shown in FIG. 3 with the use of a setting lamp 20. The settingmay be either an ultraviolet photosetting or a radical polymerizationsetting by electron rays or the like. Ultraviolet rays are projectedfrom, for example, a xenon lamp, mercury-vapor lamp, metallic halidelamp, chemical lamp, carbon arc lamp, or the like. In view of therapidly of the resin layer setting, a high-pressure mercury-vapor lamp,chemical lamp, or the like having a peak at 365 mμ wave length ispreferably used as the light source 20.

As electron rays, those of electrocure (scanning) type or electrocurtaintype may be used.

With the aim of speeding up the forming of the layer, the foregoingsetting process may be carried out during the application of the resinsolution 12. As indicated by chain line in FIG. 2, an ultraviolet raysource, an electron ray irradiating device, or the like may be providedas shown at 20 immediately adjacent to the dryer 18 thereby performingdrying and setting for each rotation of the base. In this case, however,surface smoothing such as polishing and grinding may be required laterin some instances because the setting is accomplished before slightundulations, which have been caused by the scraping of the blade orroller 16 during the resin application, are sufficiently levelled.

The resin layer thus set is thereafter subjected to surface smoothing.The gravure printing belongs to so-called intaglio printing in which theink on non-image parts is scraped off by a doctor blade, and the inkretained in the cells is transferred to paper. For this reason thesmoothness of the cylinder surface must be of very high accuracy, ofdeviations of less than 1μ, preferably less than 0.5μ.

The aforementioned coating according to the present invention providesthe smoothness of the resin layer of an accuracy close to or almost thesame as that mentioned above. Accordingly, this surface smoothing iscarried out with a very simple operation as necessary as, for example,when sufficient levelling is not attained in the coating process.

The surface smoothing is performed by, for example, sandpapering,buffing, cutting tool grinding or the like. In any case, a very smallamount of grinding or cutting is needed.

The gravure printing blank obtained in this way is subsequentlysubjected to the electronic engraving or hand engraving whereby gravurecells with varying size and depth are formed in the set resin layer 14according to the tone of the original.

The resin layer 14 set by light, electron rays or the like is superiorin engraving quality to thermoplastic resin, and almost no burrs andbreaks are produced around the cells during engraving thereof. Theelectronic engraver is provided with a burr-cutting knife called a burrcutter, but there is no need for the operation of this burr cutter forthe engraving of the resin layer as set according to the invention.However, the engraving property is further improved by carrying out,after the setting process, a baking step according to necessity in whichthe resin layer is placed in an atmosphere of about 100° C. to stabilizethe hardness thereof.

The cylinder after being engraved is proofed and, if necessary,corrected and is thereafter mounted as a printing cylinder on a rotarypress to be used for gravure printing.

In the apparatus shown in FIGS. 1 and 2, the resin solution retainer 16is a roller, but it may be in the form of a blade. FIG. 4 shows anapparatus for applying resin solution wherein a blade-type retainer isused.

In this figure, the blade-type retainer is shown at 16A. The retainer16A is held adjustably by a support 20 which is in turn movable along aslot 21 to be fixed at any height along the slot. A fixing bolt 22serves to tighten the support 20 at any position along the slot.

The slot 21 is formed in a substantially vertical lever 24 pivotallysupported at 26 on a frame 27. A stop 28 functions to limit the swingingmovement of the lever 24 away from the cylindrical base 10 which isdriven by a motor M₁ via transmission means 30. A weight 31 exerts aforce via a string 32 on the lever 24 to cause the same to swing towardthe base 10, thereby to urge the tip edge of the blade retainer 16A tocontact the surface of the base 10.

A handwheel 34 has a screwed shaft 35 rotatably supported in the frame27. A nut 36 is in engagement with the shaft 35 and can be moved alongthe shaft by turning the wheel 34. The nut 36 supports thereon a mount37 on which is supported a motor M₂. The output shaft of the motor M₂ iscoupled to an eccentric cam 38 via a speed reduction mechanism notshown. A cam follower 39 is fixed to the lever 24 and is in contact withthe cam 38. The lever 24 supports thereon a levelling roller 40 forlevelling the resin solution layer applied to the surface of the base10. As in the embodiment shown in FIGS. 1 and 2, the apparatus shown inFIG. 4 has a dryer 18 disposed at the side of the base 10 remote fromthe resin solution retainer 16A.

At the beginning of the resin solution applying step, the tip edge ofthe blade 16A is in sliding contact with the cylindrical surface of thebase 10, so that the application of the resin solution starts withalmost zero thickness of the applied layer. As the base 10 is rotated bythe motor M₁ in the direction of the arrow, the motor M₂ is operated torotate the eccentric cam 38 very slowly. Since the cam 38 is socontoured and disposed that its radius acting on the lever 24 increasesgradually, the lever 24 is swung very slowly away from the base 10 sothat the tip edge of the blade 16A also moves very slowly away from thebase surface. As a consequence, the spiral application of the resinsolution to the base surface is carried out.

It will be apparent that in the apparatus shown in FIG. 4 the blade 16Acan be replaced by a rollertype retainer as shown in FIGS. 1 and 2.

EXAMPLE

A cylindrical base structure was used as a metal cylinder with acircumference of 660 mm and a length of 700 mm. This metal cylinder waspreviously heated to 40° C. After a roller-type resin solution retainerwas brought in contact with the cylinder, a low viscosity resin liquidwas supplied and applied as a coating onto the metal cylinder. Thisapplication of the resin liquid was made with the metal cylinderuniformly rotated at 3 rpm under heating and with the blade moved awayfrom the cylinder at 5 to 30 μ/min.

The resin liquid was methyl alcohol solution containing 30% of aphotosetting polyamide resin (manufactured by Tokyo Oka Kogyosha, Japan)of a viscosity set at 50 cps at 25° C. The application of the resinliquid for about fifteen minutes provided a coating film of excellentlevelling having a film thickness of the order of 150μ±20μ.Subsequently, the coating film was subjected to photosetting withrespect to the whole surface thereof by a light source of ahigh-pressure mercuryvapor lamp of 2.1 KW for about 20 minutes. Theresincoated cylinder thus obtained was mechanically engraved by means ofan electronic engraver, Helio Klischograph K 200 type (trademark of theproduct manufactured by Dr.-Ing. Rudolf Hell GmbH, West Germany). In theengraving, 70 lines per centimeter were used, and the working standardwas the same as that of the conventional copper-plated cylinder, but theburr cutter was not used.

Upon proofing of the engraved printing cylinder, an excellent tonereproduction was noted.

Thereafter, the cylinder was mounted in a gravure rotary press, andprinting was carried out with the use of a toluene-ethyl acetate-IPAmixed solvent gravure ink and a steel doctor blade (Vickers' hardnessnumber: 550), whereupon reproduction of improved full shadow density andexcellent voluminous quality was obtained. Further no doctor scratcheswere noted with no problem involved after 400,000-meter web printing.After printing, the Ballard stripping of the resin layer was easilymade, so that the cylindrical base structural could be reused.

What is claimed is:
 1. Apparatus for applying a synthetic resin solutionspirally to the surface of a cylindrical base, comprising:means forsupporting and rotating the base; a resin solution retainer disposedalong and closely adjacent to the base to define therebetween a sump forretaining the resin solution; means for moving the solution retainerslowly away from the base to cause the resin solution in the sump toflow onto the surface of the base for application of the solution to thebase surface as a spirally laid layer, comprising a substantiallyvertical lever disposed adjacent to the base and pivotally supported atits lower end for movement toward and away from the base, said leversupporting adjustably thereon said solution retainer; means for movingsaid lever and thereby the solution retainer away from said base; anddrying means disposed along said base to dry the solution applied to thebase surface.
 2. Apparatus according to claim 1, wherein said levermoving means is a motor-driven eccentric cam acting on the lever. 3.Apparatus according to claim 1 or 2, wherein said solution retainer is aroller.
 4. Apparatus according to claim 1 or 2, wherein said solutionretainer is a blade.
 5. Apparatus according to claim 1, wherein saidlever has a slot at its upper end part and said solution retainer issecured to a support which is adjustably slidable along the slot. 6.Apparatus according to claim 2, wherein the lever has a follower to beacted upon by the eccentric cam.
 7. Apparatus according to claim 6,comprising means for acting on the lever in such a manner that thefollower is urged against the cam.
 8. Apparatus according to claim 2,comprising a substantially horizontal screw shaft having a handwheel, anut engaging the screw shaft, and a mount secured to the nut andsupporting thereon a motor for driving said eccentric cam.